Google, drawing from its $56.5 billion cash pool, is spending more money than five of its biggest U.S. competitors combined to buy into new markets as growth in Web advertising slows.

Including this week's announced deal to buy Nest Labs Inc. for $3.2 billion in cash, Google has spent more than $17 billion in the past two years to purchase hardware, software and advertising-technology companies, according to data compiled by Bloomberg. Apple, Microsoft, Facebook, Amazon.com and Yahoo have spent less than $13 billion in total to buy companies in the same period, based on deals with disclosed prices.

The spending blitz, which is mostly in cash instead of stock, underlines how Google is paying top dollar to expand its reach and acquire the talent necessary to push deeper into areas such as smartphones and Web-enabled gadgets. While Google has dominated Internet search, a business that generates billions of ad dollars each quarter, the company is seeking new revenue from other sources and turning to its cash hoard to provide an advantage.

Google's cash and equivalents jumped 24 percent from a year earlier in the third quarter to $56.5 billion, while net revenue increased by 5.2 percent to $11.9 billion. Google gets 84 percent of sales from Internet ads, even after diversifying into hardware and other areas.

Revenue growth slowed last year and is expected to do so again in 2014 based on analysts' estimates as more online activity shifts from personal computers to smartphones, tablets and other connected devices. That hurts Google's sales because mobile ads typically cost less, and because search is less prominent on other devices. By 2017, PCs will account for 13 percent of connected-device shipments worldwide, down from 29 percent in 2012, according to researcher IDC. Tablets will make up 17 percent by 2017, and smartphones will account for 71 percent, IDC said.

Google's all-cash acquisition of Nest, its third biggest, gives the company a maker of smart thermostats and smoke alarms built by Tony Fadell, who previously helped Apple co-founder Steve Jobs create the iPhone. Fadell's co-founder Matt Rogers is also an Apple alumnus, as are at least 97 Nest employees, according to LinkedIn Corp. That's talent Google can put to use.

Among top U.S. competitors, Microsoft has been the biggest buyer in the past two years after Google, spending about $9 billion. Most of that was on the pending $7.4 billion purchase of Nokia Oyj's handset unit and the $1.2 billion acquisition of business-software provider Yammer Inc.

Facebook's biggest deal was mobile photo-sharing application Instagram for more than $700 million in 2012.

Amazon's only notable deal in the past two years was for robotics company Kiva Systems, which cost about $700 million. Yahoo's disclosed deals total about $1.2 billion, with most of that spent on blogging startup Tumblr last year.

Apple's spending amounted to less than $1 billion since early 2012, with about $350 million spent on fingerprint-technology company AuthenTec.